Hitherto, as a compound releasing a photographically useful group corresponding to the density of images upon development, there have been known (1) hydroquinone derivatives releasing a development inhibitor corresponding to the density of images at development (so-called DIR hydroquinone), (2) hydroquinone derivatives releasing a silver halide solvent corresponding to the density of images, and (3) hydroquinone derivatives or sulfonamide phenol derivatives releasing a diffusible dye corresponding to the amount of developed silver.
Examples of the DIR hydroquinone are described in U.S. Pat. Nos. 3,379,529, 3,620,746, 4,377,634, Japanese Patent Application (OPI) Nos. 129536/74, 153336/81, 153342/81, etc. (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). Examples of the hydroquinone derivative releasing a silver halide solvent are described in U.S. Pat. No. 4,459,351, etc. Also, examples of the hydroquinone derivative releasing a diffusible dye are described in U.S. Pat. Nos. 3,698,897, 3,725,062, etc., and examples of the sulfonamide phenol derivative releasing a diffusible dye are described in Yuuki Goosei Kagaku Kyokai Shi (Journal of the Society of Organic Synthesis Chemistry), Vol. 39, p. 331 (1981), Kagaku no Ryoiki (Domain of Chemistry), Vol. 39, p. 617 (1981), Kinoo Zairyo (Functional Materials), Vol. 3, p. 66 (1983), Photographic Science and Engineering, Vol. 20, p. 155 (1976), Angew. der Chemie, International Edition in English, Vol. 22, p. 191 (1983), Yuuki Goosei Kagaku Kyokai Shi (Journal of the Society of Organic Synthesis Chemistry), Vol. 40, p. 176 (1982), Nikka Kyo Geppo (Monthly Bulletin of the Chemical Society of Japan), Vol. 35 (11), p. 29 (1982), etc.
The known compounds described in the above patents, etc., have been widely used according to the photographic effects of the photographically useful groups released from the compounds, but the functions required for the oxidation reduction mother nucleus which is a minimum unit performing the oxidation reduction reaction for releasing photographically useful groups have many common points. This is because, recently, it has become more important as a point required that high-quality photographs be obtained quickly, simply, and stably, and the above-described compounds are used as elements for fulfilling such a purpose or assisting the attainment of the purpose. That is, the common performance required for the oxidation-reduction mother nuclei of the above-described compounds is the point that the photographically useful group can be released quickly in a short period of time with good timing and good efficiency.
Then, the performance required to these the oxidation reduction mother nuclei is described below in more detail. Firstly, in order that these oxidation-reduction nuclei show a sufficient activity during the development process, it is required that the speed of causing a cross-oxidation reaction with the oxidation product of a developing agent or an auxiliary developing agent formed during development or the speed of becoming an oxidation product thereof directly or by reducing a silver halide or other silver salts is sufficiently high. Secondly, it is required that the photographically useful group is released from the oxidation product of the oxidation-reduction nucleus thus formed at high speed and the release of the group occurs efficiently. Also, thirdly, it is required that these oxidation-reduction mother nuclei be sufficiently stable during storage, and do not give photographically undesirable influences by being decomposed by oxygen in air or by other materials.
Regarding the first point noted above, it is generally considered to be possible to increase the oxidation speed of the oxidation-reduction mother nucleus by reducing the oxidation potential of the oxidation-reduction mother nucleus. However, the reduction of the oxidation potential is generally accompanied by the increase of the speed of being oxidized by oxygen in air as described in Journal of American Chemical Society, Vol. 60, p. 2084 (1938), and hence gives an undesirable result considering the third point noted above. Accordingly, it is difficult to obtain both the high reactivity during processing and stability during storage by reducing the oxidation potential for realizing the high reactivity during processing.
On the other hand, from the viewpoint of preventing the occurrence of oxidation by oxidation in air, the protection of oxidation-reduction mother nuclei is frequently performed. Such protection can be relatively effectively used with the pH of a developer is high, when the specific accelerating effect by the processing composition as described in Japanese Patent Application (OPI) Nos. 19703/84, 201057/84, etc., can be ideally utilized, or when the processing period is very long. However, in general, if the oxidation-reduction mother nuclei are protected, additional one stage or more reaction numbers are required for the realization of the function of the oxidation-reduction nuceli. Accordingly, it requires a long period of time to realize the function of the oxidation-reduction nuclei since the initiation of a development proces, whereby it becomes difficult to obtain a sufficient function thereof in a short period of processing. Thus, there are many difficulties for obtaining both the quick processing and the sufficient realization of the function thereof although a further increase of the processing speed has now been desired.
Regarding the second viewpoint, that is, the speed and the efficiency for releasing a photographically useful group from the oxidation product of an oxidation-reduction nucleus, the compounds described in the above-described patents, etc., are insufficient, and hence if the speed and the efficiency can be increased, it can greatly accelerate the realization of the function thereof.